Owing to the drawbacks of non-renewable energies, such as those based on the combustion of fossil fuels or nuclear energy, major efforts have been made to develop what are known as renewable energies, amongst which those based on the use of the motion of a fluid to drive an electrical power generator are found. For example, devices known as multi-blade aerogenerators exist, which make use of the wind to rotate the rotor of an electric generator. However, these aerogenerators, which have had great success worldwide and, in many countries, produce a major share of the electrical energy consumed, usually have a large number of moving parts, many of which come into contact with each other in a rotating manner, thus implying, amongst other things, relatively high maintenance costs, owing to the consumption of lubricants, component wear, etc. In some cases, the high speed of the blades may also be a problem, since they may impact bird life.
As an alternative to multi-blade aerogenerators with rotating electric generators, the use of generators based on the use of piezoelectric elements or materials for converting mechanical energy into electrical energy has also been proposed. For example, FR-2922607-A1 discloses an electrical power generator in which a type of pole is supported on piezoelectric elements, such that when the pole is driven or moved by the wind, the movement of the pole is converted into electrical energy through piezoelectric elements.
On the other hand, CN-201818437-U discloses an electrical power generator for powering sensors and systems with low power consumption, which is also based on a rotor with blades. The rotor is provided with magnets that rotate with the rotor and which interact with magnets coupled to piezoelectric elements such that the rotation of the rotor results in a force on the piezoelectric elements, such that the rotation of the rotor is converted into electrical energy.
JP-2006-158113-A describes another mechanism for converting mechanical energy into electrical energy using a piezoelectric element attached to a magnet.
Moreover, JP-2006-132397-A describes the use of the Karman vortices in water to make a column that is introduced in water vibrate, which is coupled to a piezoelectric plate. Similarly JP-2006-226221-A and WO-2012/017106-A1 refer to electrical generators based on Karman vortices.
For example, WO-2012/017106-A1 describes an electrical power generator driven by wind with a pole made up of a plurality of elements with high electromechanical coupling, a term which encompasses piezoelectric elements. The pole has a section and configuration that deliberately transforms the flow of stationary and laminar air into a turbulent flow, wherein eddies or vortices appear in a synchronised manner throughout the length of the pole. Therefore, the pole sustains two forces, namely, a drag force in the same direction as the wind and a lift force produced in a direction perpendicular to the direction of the wind, the direction of which changes sign, with a frequency that corresponds to the frequency of the appearance of new vortices and which can be calculated using the following formula:Fv=S*V/d, where Fv is the frequency of appearance of vortices, V the velocity of the air and d the characteristic dimension of the pole, for example, in the case of a pole having a circular cross-section, the diameter of the pole. S is Strouhal's dimensionless number. Given that the velocity of the air increases with height, according to the Hellmann exponential Law, to achieve synchronisation in the appearance of vortices, WO-2012/017106-A1 proposes an increase in pole diameter with the increase of height.
WO-2012/017106-A1 does not explain in detail how the movement of the pole is converted into electrical energy. Nonetheless, given that it is indicated that the pole itself is made up of a plurality of elements with high electromechanical coupling, it is understood that it is the swaying of the pole that deforms the elements thereby generating a power differential between the surfaces of the affected elements. On the other hand, WO-2012/017106-A1 proposes active modulation of the apparent Young's modulus or apparent elasticity modulus of the pole, by varying the electrical voltages to which the elements with high electromechanical coupling are subjected.
WO-2014/135551-A1, which is incorporated herein by reference, discloses other examples of electrical power generators based on Karman vortices, in which the oscillating movement of a pole is converted into electrical energy by piezoelectric systems. It also explains how the natural frequency of oscillation of the pole can be modified by applying a voltage to a piezoelectric material that surrounds an elastic core of the pole.
This type of generator based on the Karman vortices can operate without bearings, gears and lubricants and does not require a start system.
Although the use of piezoelectric elements may seem to be an ideal solution to the problem of tuning the pole to variations in the speed of movement of the fluid, for example, the wind speed and also for converting an oscillatory and non-rotational movement—such as the movement naturally generated by the Karman vortices—into electricity, it has been found that it may be interesting to find technically and economically feasible alternatives to the use of abundant piezoelectric material.
US-2008/0048455-A1 describes another example of electrical generator based on Karman vortices, based on the use of a gyroscopic electrical generator. However, this type of mechanism involves rotating generation elements requiring the corresponding maintenance.
WO-2012/066550-A1 describes another generator based on the use of Karman vortices, with an active control of the frequency of vortex formation to adjust it to the natural frequency of oscillation of the capture element.
US-2005/0230973-A1 discloses another vibration based power generator including a vortex shedding device. The described embodiments relate to the context of energy production in a well, taking advantage of the fluid produced from a formation. Different means for converting vibration into electric power are disclosed, including piezoelectric means and magnets interacting with coils.
JP-2012-151985-A and JP-2012-151982-A disclose vibration power generators based on magnets oscillating in relation to a coil, and including means for changing a resonance frequency.
JP-2001-157433-A discloses several different power-generating devices, one of which features a cylinder with an upper part fixed to a support. The cylinder is a vibrating body and a permanent magnet is attached to the lower part of the cylinder. This permanent magnet is related to another, stationary, permanent magnet in a manner such that the repulsive force between these permanent magnets gives rise to a tensile force on the cylinder. A coil is wound around one of the permanent magnets. Bending of the cylinder between its ends caused by a flowing fluid causes the permanent magnets to approach each other and changes the magnetic flux passing through the coil.